More than 20,000 foreigners from 90 countries, including thousands from the West, have joined militant factions in Syria such as the Islamic State, a top counterterrorism official told U.S. lawmakers Wednesday.

The prepared testimony by Nicholas Rasmussen, director of the National Counter Terrorism Center, offered no details on how the figure was reached. It also gave no clear picture on the estimated 150 Americans the report claims have traveled to Syria or attempted to make contact with extremist groups.

But the comments — just hours after President Obama asked Congress for formal authority to combat the Islamic State — echo worries about the recruiting reach of the Islamic State in Syria and Iraq.

European authorities, in particular, have raised alarms about suspected Islamist militants returning to home countries after time in Syria and elsewhere.

Rasmussen told the House Homeland Security Committee an estimated 3,400 suspected fighters or sympathizers have traveled to Syria from Western countries, including the 150 from the United States.

That overall figure represents a 70 percent jump in the past four months, he said.

“The rate of foreign fighter travel to Syria is unprecedented. It exceeds the rate of travelers who went to Afghanistan and Pakistan, Iraq, Yemen, or Somalia at any point in the last 20 years,” Rasmussen said in the prepared remarks.

The Islamic State holds large portions of territory in Syria. But other militant factions also have footholds, including the al-Qaeda-linked Jabhat al-Nusra, which is fighting the government of Syrian President Bashar al-Assad.

“The battlefields in Iraq and Syria provide foreign fighters with combat experience, weapons and explosives training, and access to terrorist networks that may be planning attacks which target the West,” Rasmussen said.

The head of the House Homeland Security Committee, Rep. Michael McCaul (R-Texas), said groups such as the Islamic State should be regarded as enemy “armies.”